diff --git a/bin/dup b/bin/dup
index e7880ec1..13e31b25 100755
--- a/bin/dup
+++ b/bin/dup
@@ -21,7 +21,7 @@ def _set_env(index):
     for target_env_raw_name in target_environ_raw_names:
         env_value = os.getenv(target_env_raw_name)
         target_env_name = re.findall(r"^DST_\d+_(\w+)$", target_env_raw_name)[0]
-        os.putenv(target_env_name, env_value)
+        os.environ[target_env_name] = env_value
 
     # Expand shell commands from environment options
     # this resolves environment variables used in the string